Journal of Experimental Marine Biology and Ecology 443 (2013) 21–26

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Journal of Experimental Marine Biology and Ecology

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Olfactory discrimination in juvenile coral reef fishes:Response to conspecifics and corals

Amy G. Coppock a,b,⁎, Naomi M. Gardiner a, Geoffrey P. Jones a,b

a School of Marine and Tropical Biology, James Cook University, Queensland, 4811, Australiab ARC Centre of Excellence for Coral Reef Studies, James Cook University, Queensland 4811, Australia

⁎ Corresponding author at: School ofMarine and TropicaQueensland, 4811, Australia. Tel.: +61 747814345; fax: +

E-mail address: amy.coppock@my.jcu.edu.au (A.G. C

0022-0981/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.jembe.2013.02.026

a b s t r a c t

a r t i c l e i n f o

Article history:Received 19 April 2012Received in revised form 11 February 2013Accepted 12 February 2013Available online xxxx

Keywords:Branching coralChaetodontidaeChemosensory cuesHabitat selectionOlfactionPomacentridae

Coral reef fish use olfaction to respond to a variety of chemical cues that allow them to detect predators, thepresence of resident conspecifics and the ‘smell’ of reef water. However, whether olfaction is utilised by ju-venile reef fish for discerning among the multiple microhabitat types present on the reef is not known. Ad-ditionally the relative importance of chemical cues emitted from habitat types versus those from residentindividuals to juveniles has not been assessed. The ability to distinguish and use such cues could be criticalin determining spatial distributions of juveniles across coral reef areas. Here we test olfactory preferencesfor conspecifics, coral health and different branching coral species in newly recruited juveniles of coral reeffishes. Newly settled juveniles of three common coral associated species in Kimbe Bay, Papua New Guinea,Dascyllus melanurus, Chrysiptera parasema and Chaetodon octofasciatus, were subjected to a series of pairwiseolfactory choice tests using two-channel choice flume. All three species exhibited a significant preference forthe scent of conspecifics (60–70%) and live coral (60–70%) over water with no associated reef cues. All spe-cies strongly avoided the odour of degraded coral (≥80%). Only one species, D. melanurus showed olfactorydiscrimination among branching coral species, favouring Pocillopora damicornis over Acropora spp. Our re-sults indicate that olfactory preferences for both conspecifics and live coral may combine to determine juve-nile and recruitment distribution patterns in these species and local population declines in response to coraldegradation but do not necessarily contribute to specific coral habitat associations.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Strong associations between juvenile fishes and particular habitatfeatures have recently been invoked in the explanations of decliningreef fish abundance and diversity in response to reef degradation(Coker et al., 2009; Jones et al., 2004; Wilson et al., 2008). However,the sensory mechanisms involved in habitat selection or avoidance,and consequently the process by which fish respond to degradedreef habitats is poorly understood. Olfactory senses are critical indirecting late stage larvae towards suitable reef environments suchas lagoonal areas, natal sites, and away from non-reef locations(Dixson et al., 2008; Gerlach et al., 2007; Lecchini et al., 2005a). It islikely that olfaction also assists fish in selecting among the diversityof substrate types present on the reef, discerning healthy or un-healthy coral habitats and thereby determining microhabitat distri-butions. The detection and use of olfactory cues are particularlyimportant for coral specialist reef fish species, which are most atrisk of habitat loss (Wilson et al., 2008).

l Biology, James CookUniversity,61 747815511.oppock).

rights reserved.

A variety of cues are used by reef fish to recognise, locate and nav-igate towards appropriate habitats, including: chemical, auditory,solar directional, rheotactic, magnetic, wave motion, visual and ther-mal cues (Arvelund and Takemura, 2006; Kingsford et al., 2002; Lara,2008; Myrberg and Fuiman, 2002). Of these chemical signals aredeemed to be one of the most important cues used by fish choosingparticular microhabitats, because settlement predominantly occursat night when vision is ineffective (Døving et al., 2006; Sweatman,1988). Chemical cues refer to those distinguished via olfaction andgustation. In many cases, however, it is thought that the primary indetecting chemical cues is olfaction (Dixson et al., 2011; Leis et al.,2011), principally as the olfactory system begins to function and pro-vide responses by juveniles to chemical signals before similar pro-cesses occur via the taste system (Kasumyan, 2011). Larval andjuvenile fish can use olfactory cues to differentiate between water ofoceanic origin and that derived from areas of reef (Atema et al.,2002; Dixson et al., 2008; Gerlach et al., 2007), discern predators(Dixson et al., 2010; McCormick and Manassa, 2008; Wisenden,2000) and detect the presence of conspecifics (Lecchini et al., 2005a,b, 2007; Sweatman, 1983, 1985, 1988). Their response to thesecues enables successful settlement into reef habitats. Many reef fishspecies microhabitat associations appear to be determined in earlypre- and post-settlement periods, after which individuals remain

Fig. 1. Two-channel choice flume used for pairwise choice tests (Atema et al., 2002). Rindicates the release position of test fish. Arrows indicate the direction of water flowfrom alternate water sources (A & B).

22 A.G. Coppock et al. / Journal of Experimental Marine Biology and Ecology 443 (2013) 21–26

permanently associated with the same substrate types (Bonin et al.,2009; Danilowicz, 1996; Öhman et al., 1998).

Conspecific chemical cues have long been regarded as important in anumber of coral reef fish species (Sweatman, 1985). For some, conspe-cific cuesmay bemore important than habitat cues (Gardiner and Jones,2010). The presence of conspecifics has been shown to attract settlingfish via a combination of visual and olfactory cues (Booth, 1992;Lecchini et al., 2005a; Sweatman, 1983, 1985, 1988). However, thesole use of olfaction by reef fish to detect conspecific cues has notbeen tested. To a recruit the presence of conspecifics indicates that aparticular site is a suitable living environment. However, it is the behav-iour of residents towards the recruit that will influence the latter'sdecision to use the same location. For territorial species the presenceof adult conspecifics is thought to signal a poor location due to thehigher likelihood of resource competition and subsequent predationmortality (Russell et al., 1974; Sale, 1976, 1978; Sale and Dybdahl,1975, 1978;Ward et al., 2006). However, in a gregarious species recruitsare expected to cue towards adult conspecifics and subsequently settlewith them (Booth andWellington, 1998; Hoare et al., 2004; Sweatman,1983, 1985, 1988). Olfactory responses in territorial species towardsconspecifics are, therefore, expected to be more negative than those ofa gregarious species.

Still, it is not exclusively the presence of resident fishes that is likelyto affect the choice of settlement site. Habitat quality cues are alsoessential settlement cues for many reef fish, particularly for obligatecoral dwelling species that settle on live, branching coral and avoiddead or degraded corals (Feary et al., 2007b; Öhman et al., 1998). Al-terations to the health of coral reefs, such as reductions in coralcover, are closely linked to eventual declines in reef fish abundanceand diversity (Booth and Beretta, 2002; Feary et al., 2007a; Mundayet al., 2009; Pratchett and Berumen, 2008). The effects of habitat deg-radation are greatest for coral dependent species (Booth and Beretta,2002; Feary et al., 2007a; Munday, 2004; Munday et al., 2009;Pratchett and Berumen, 2008), contributing to recruitment failureand subsequent declines in adult fish assemblages as well (Jones etal., 2004). Whether olfactory mechanisms are critical in habitat se-lection at settlement, and in particular, whether fish can distinguishdegraded versus healthy coral via olfaction are not yet known. Inves-tigating such mechanisms is essential in understanding resource useand the processes through which reef fish are affected by habitatdegradation.

Recent work on habitat selection suggests that many reef fish dis-criminate not just between live and degraded coral, but also amongcoral species. Several studies indicate that some reef fishes stronglyprefer certain coral species over others (Bonin et al., 2009; Gardinerand Jones, 2005; Munday, 2000, 2004; Munday et al., 1997). In locat-ing suitable recruitment sites chemical cues emitted from individualcoral species may be detected via olfaction and consequently usedto direct site choice by searching fish. Several reef fish groups are al-ready known to use olfaction in distinguishing between watersources from oceanic versus reef origin (e.g. Apogonidae: Atema etal., 2002) and island versus non-island reefs (Amphiprion percula:Dixson et al., 2008). At a finer scale, anemone fish recruits (A. percula)can also smell the difference between water containing their pre-ferred anemone species versus water without it (Dixson et al.,2008). Given the coral specific habitat preferences of many juvenileand adult reef fish species, it is likely that their olfactory abilities ex-tend to discrimination among coral species, and in combination withconspecific preferences, direct spatial distributions.

This study investigates the ability of juvenile coral reef fishes touse chemical discrimination to respond towards conspecifics, coralhealth and different coral species. We tested whether recentlyrecruited juveniles can distinguish between (1) the presence and ab-sence of conspecifics, (2) between healthy and degraded coral tissue,and (3) different branching coral species, solely via chemical cues.The study focused on the juveniles of three common coral reef fish

species known to strongly associate with live branching coral habitatsin Kimbe Bay, Papua New Guinea. These were: Dascyllus melanurus,Chrysiptera parasema and Chaetodon octofasciatus. Juvenile and adultdistributions have indicated that conspecific and coral specific prefer-ences are likely for all three species, with each predominantly beinglocated in small aggregations on 1–2 coral species and not randomlydispersed among available habitats (Bonin et al., 2009; Breder andRosen, 1966). Previous research on coral reef fish indicates that olfac-tory preferences used by settlement stage ‘naïve’ larvae are the sameas those present in newly recruited juveniles (Dixson et al., 2008).This paper considers olfactory responses by the latter with a view toinferring the use of cues during both pre- and post-settlement stagereef fish.

2. Materials and methods

2.1. Study location and species

The study was carried out in Kimbe Bay (5°12.530 S, 150°22.801 E)on the island of NewBritain, PapuaNewGuinea. Aquaria based olfactionexperiments were carried out over a three-week period between 11March and 4 April 2010 at Mahonia Na Dari Research and ConservationCentre.

The focal species for the study were the Blacktail Dascyllus(D. melanurus), the Goldtail Demoiselle (C. parasema) and theEight-banded Butterfly fish (C. octofasciatus) — all species specialiseon live branching coral (Berumen et al., 2005; Bonin et al., 2009;Pratchett and Berumen, 2008).

Juveniles (b2.5 cm SL) were collected from small coral heads oninshore reefs (2–20 m depth) using low dose clove oil anaestheticand hand nets. Low dose clove oil was prepared by mixing one partclove oil with two parts of low-grade ethanol and three parts of sea-water. Following their capture fish were allowed to recover for atleast 2 h before being used in olfactory discrimination trails. Recruitswere housed in small groups of conspecifics, in aquaria up until thispoint. All fish showed active swimming behaviour in holding aquaria,indicative of recovery from anaesthetic. Newly recruited juvenileswere used instead of ‘naïve’ larvae caught in light traps as it allowedfor a greater number of samples to be collected within the period oftime available.

2.2. Apparatus and trial design

The responses of juvenile D. melanurus, C. parasema andC. octofasciatus to olfactory cues were tested using a two-channelchoice-flume (13 cm×4 cm), developed by Atema et al. (2002)(Fig. 1). The apparatus allows pairwise choice experiments in whichindividual fish can move freely between water flowing from two dif-ferent sources. Water from two alternate sources was gravity fedfrom buckets, into the choice-flume, which was partitioned alonghalf its length. Recruits were released in the downstream end of theflume (R in Fig. 1), where the exploration of both water sources was

23A.G. Coppock et al. / Journal of Experimental Marine Biology and Ecology 443 (2013) 21–26

possible, allowing for the selection of a preferred source. Water flowwas maintained at a constant speed of 100 ml min−1 throughout alltrials. Dye tests were conducted before each trial to ensure that dis-tinct and parallel water flows were exhibited by each of the channelsand that no turbulence or eddies were present.

For each trial, a single recruit was placed in the downstream endof the flume and left to acclimate for 2 min. During this period thefish was able to swim throughout the chamber. At the end of the ac-climation period, the position of the fish within the chamber wasrecorded at five-second intervals for the duration of 2 min. This wasfollowed by a one-minute rest period, during which the water sources(A & B) were switched, providing a control for potential chamber sidepreferences. Following this switch the entire test, including the accli-mation period was repeated. Any fish that did not swim throughoutthe chamber during the acclimation period were removed from thetrials, as it was not deemed to have assessed the choices available.

In each trial recruits were given the choice between either a watersource that had been treated with a specific chemical cue and a watersource that had not been treated with any chemical cues (the control);or two water sources that had been treated with chemical cues derivedfrom differing species of coral. Offshore seawater was used as a base‘control’water source and collected daily at a distance of approximately1 km away from any nearby reefs.

Initial trials involved validating the chamber choice technique forall species. A series of blank trials was conducted to test for any pref-erence behaviour, towards one side of the chamber in the absence ofexperimentally added chemical cues. During control trials newlyrecruited D. melanurus, C. parasema and C. octofasciatus spent equalamounts of time on both sides of the chamber (Fig. 2). These resultsindicated the use of untreated water in subsequent trials as an appro-priate control and that no side preferences were apparent with regardto the chamber itself.

All odour discrimination trials were run on 10–20 individual fishof each species per treatment. No fish was used more than once.

2.3. Experimental treatments

Experimental trials were run testing preferences towards (1) con-specific cues, (2) different coral genera, and (3) coral health status. Ol-factory preferences for conspecific cues were tested by comparingchoices between the conspecific scented water and offshore waterwith no associated reef cues. Discrimination among coral species was

Fig. 2. Olfactory response of Dascyllus melanurus, Chrysiptera parasema and Chaetodonoctofasciatus in blank control trials. Columns show the mean percentage of time (±SE)that recruits spent in untreated water streams on either side of the flume. The greybars are representative of the left-hand side of the flume, whilst the white bars repre-sent the right-hand side. P value derived from the KS tests denotes any significantdifferences.

assessed by comparing choices between the two sources of coral scentedwater; these were Acropora spp. versus Porites cylindrica, Acroporaspp. versus Pocillopora damicornis, Acropora spp. versus Anacroporamathaii, and P. damicornis versus Seriatopora hystrix. All coral colo-nies used in odour treatments were branching corals. Acropora coralswere bottlebrush species (e.g. Acropora aculeus, Acropora carduus,Acropora hyacinthus). Comparison of olfactory preferences for coralhealth state involved comparing choices towards (1) live coral ver-sus untreated water and (2) degraded coral versus untreatedwater. Healthy and degraded Acropora spp. or P. damicornis coralfragments were used to create the coral treatment waters.

2.4. Treatment preparation

Conspecific treatment water was prepared by holding 10–15 adultand larger juvenile conspecifics in 50 l of offshore water, with an airsource, for 24 h. Likewise, coral treatment water was prepared bysoaking small live coral colonies (10 cm×10 cm) in 20 l of offshorewater for a period of 2 h. Degraded coral treatment water was pre-pared in a similar manner to the coral treatment water. Specifically,small, Acropora spp. colonies (10 cm×10 cm) were soaked in 20 l ofoffshore water, for a period of 24–48 h. During this time coraldisplayed copious mucus production, discolouration of tissue and/orbleaching. Thus the degraded coral treatment contained decayingcoral mucous and emitted a strong odour. Excess mucous was re-moved from the surface of the water of the treatment prior toconducting the trials. This prevented any blockages from occurringwithin the apparatus set up.

2.5. Statistical analysis

Kolmogorov–Smirnov (K–S) tests were used to compare the totalproportion of time that individual recruits spent in the differentstreams of water (sensu: Dixson et al., 2010; Munday et al., 2009).The time spent in treatment water was recorded for each individualby summing the number of 5-second intervals a fish spent in thetreatment water over the total 4-minute period (max count: 48). Adistribution of counts was then compiled per trial with 10–20 repli-cate values each. Treatment distributions were then compared tothe control distributions for each species. Control distributions werethe times collated from the ‘blank’ trials (n=10–20 per species).For consistency's sake and to avoid observer bias, this control dataonly included counts recorded form the left side of the choice chamber.The null hypothesis was that observed and expected distributionswould not differ significantly. For trials in which two coral sourceswere used and for the blank trials Kolmogorov–Smirnov tests comparedthe proportion of time spent in either water treatment.

3. Results

3.1. Conspecific cues

All three species showed substantial preferences towards conspe-cific odours (Fig. 3). D. melanurus recruits spent 63% of their time inconspecific treated water rather than the untreated offshore water(KS: 0.533, pb0.005). Likewise, significant preferences for chemicalcues from conspecifics were detected for C. parasema (KS: 0.667,pb0.001) and C. octofasciatus (KS: 0.700, pb0.025), which spent anaverage of 65% and 70% of their time in conspecific-soaked water,respectively.

3.2. Coral health

All three species showed strong reactions towards differences incoral health. When trials were run comparing choices between livecoral odours or untreated water, a preference for water containing

Fig. 3. Response ofDascyllus melanurus, Chrysiptera parasema and Chaetodon octofasciatusto olfactory cues from conspecifics. Columns show the mean percentage of time (±SE)that recruits spent in conspecific treated water (grey bars) versus control water withno cue (white bars). P value derived from the KS tests denote any significant differences;* pb0.05, ** pb0.01, *** pb0.001.

Fig. 5. Response ofDascyllus melanurus, Chrysiptera parasema and Chaetodon octofasciatusto olfactory cues from degraded coral. Columns show themean percentage of time (±SE)that recruits spent in degraded coral treated water (grey bars) versus water containingno cues (white bars). P value derived from the KS tests denote any significant differences;* pb0.05, ** pb0.01, *** pb0.001.

24 A.G. Coppock et al. / Journal of Experimental Marine Biology and Ecology 443 (2013) 21–26

the scent of live coral was exhibited (D. melanurus, pb0.001;C. parasema, pb0.01; C. octofasciatus, pb0.0025) (Fig. 4). A strongavoidance was evident towards the water containing the odour of de-graded coral compared to untreated water. This was consistent in allthree fish species. In all trials fish spent more than 80% of the trial pe-riod avoiding this scent (Fig. 5).

3.3. Branching coral species

The majority of trials yielded no preference or avoidance reactionstowards any of the branching coral species tested. The single excep-tion to this was a significant preference by D. melanurus towards thescent of P. damicornis over that of Acropora spp. (Fig. 6, pb0.001).Here 67% of the trial was spent in association with the water inwhich P. damicornis had been soaked. However, a similar preferencereaction towards P. damicornis was not recorded when D. melanurusrecruits were given the choice between S. hystrix and P. damicornisscented waters. Here, statistically equal proportions of time werespent in water containing the P. damicornis odour and that containingthe S. hystrix odour (53:47%, pb0.001). In no other instances were anypreference or avoidance reactions prevalent throughout the trialscomparing attraction or avoidance towards specific branching coral

Fig. 4. Response ofDascyllus melanurus, Chrysiptera parasema and Chaetodon octofasciatusto olfactory cues from live coral. Columns show the mean percentage of time (±SE)that recruits spent in live coral treated water (grey bars) versus water containing nocues (white bars). P value derived from the KS tests denote any significant differences;* pb0.05, ** pb0.01, *** pb0.001.

species (Fig. 6). This lack of preference or avoidance was consistent re-gardless of whether the choice was between: Acropora spp. andP. cylindrica, Acropora spp. and P. damicornis, Acropora spp. andAnacropora mathaii, or P. damicornis and S. hystrix.

4. Discussion

Chemical cues are one of themainways inwhich juvenile reef fisheslocate reef environments in which to settle (Kingsford et al., 2002). Re-sults herein are the first to reveal that olfactory discrimination in recruitfish extends to the scale ofmicrohabitat typeswithin reefs, and towardsconspecific individuals. This degree of discrimination is much finer thanpreviously appreciated. Here recruits of three common coral associatedfish species showed strong olfactory preferences towards conspecificsand live branching coral over water with no associated reef cues. Addi-tionally all fish species avoided the smell of degraded coral. One of thespecies,D.melanurus, also preferred P. damicornis coral over bottlebrush

Fig. 6. Response ofDascyllus melanurus, Chrysiptera parasema and Chaetodon octofasciatusto olfactory cues fromdifferent branching coral species. Columns show themean percent-age of time (±SE) that recruits spent in the water containing scent of specific coralspecies. P value derived from the KS tests denote any significant differences; * pb0.05,** pb0.01, *** pb0.001.

25A.G. Coppock et al. / Journal of Experimental Marine Biology and Ecology 443 (2013) 21–26

Acropora spp. based on chemical stimuli alone. However, very little ol-factory discrimination among live branching coral species was evidentin the two other species. Current results suggest that the presence ofconspecifics and live branching coral are key drivers of olfaction basedhabitat selection in these species.

The presence of conspecifics appears to be the major cue for settle-ment site selection in all three species, with 60–70% of time in all trialsbeing spent in thewater containing the conspecific scent. This pattern isconsistent with the results of experiments by Sweatman (1983, 1985,1988), Booth (1995, 2002) and Ben-Tvzi et al. (2009) with Dascyllusaranurus, Booth (1992) with Dascyllus albisella, Døving et al. (2006)with Cheilodipterus quinquelineatus and Apogon compressus adults, andBen-Tvzi et al. (2009) withDascyllus marginatus. Likewise, a strong rec-ognition of conspecifics is acknowledged for several Chaetodontid spe-cies whereby juveniles have been shown to settle directly onto habitatsoccupied by conspecifics (Pratchett and Berumen, 2008).

Conspecifics may well be an accurate predictor of suitable habitatin terms of adequate food, shelter or lack of predators (Booth, 1992).As such strong associations with corals (particularly for butterfly fish)may be established at time of settlement, whereby larvae preferen-tially settle onto particular habitats and consequently rarely movethereafter (Berumen et al., 2005; Pratchett and Berumen, 2008). Apreference for conspecifics, particularly at times of settlement, mayalso enhance survivorship by diluting individual predation risks andincreasing predator awareness (Beukers and Jones, 1997; Booth,2002; Pitcher, 1993; Pitcher et al., 1986; Seghers, 1981). These factorswould subsequently improve future survival, growth and reproduc-tion as more time can be allocated to the latter.

All three study species preferred olfactory cues derived from livingcoral. Numerous previous studies have indicated a preference by var-ious reef fishes to the presence of live coral cover, particularly at timesof settlement (Feary et al., 2007a,b; Jones et al., 2004; McCormick etal., 2010). Feary et al. (2007a) demonstrated that a number of juve-nile Indo-Pacific coral reef fish species preferentially associated witheither live or partially degraded coral colonies within laboratoryaquaria. Likewise McCormick et al. (2010) demonstrated that boththe live coral specialist Pomacentrus moluccensis and the habitatgeneralist Pomacentrus amboinensis preferred live coral and avoidedbleached and dead coral. Indeed live coral preferences are oftenseen to occur irrespective of whether the fish is regarded as a coralspecialist or not (Jones et al., 2004). If this is the case it may accountfor the significant reactions by all fish tested to the occurrence oflive coral scent, as well as their explicit avoidance of the scent ofdegraded coral. Whilst it is acknowledged that the degraded coraltreatment water is a particularly potent treatment and as such theavoidance reaction particularly extreme, this still demonstrates thatthe use of chemical cues in orientation towards suitable areas ofreef is apparent.

This study is the first to investigate whether the chemosensory sys-tem is a key mechanism in juvenile distributions of coral specialist reeffish towards individual coral species. Our study followed up on recentevidence that found many reef fishes discriminate among differentcoral species as settlement sites (Bonin et al., 2009, 2011). The olfactionresults herein were only partially consistent with known habitat usepatterns by recruits of all three species. The damselfishD. melanurus se-lected for corals of P. damicornis spp. when tested against Acropora spp.D. melanurus preferentially inhabits P. damicornis over other species ofbranching corals (Bonin et al., 2009). Thus olfactory preference maybe the directing influence in this species degree of habitat specialisation.A sister species, D. albisella, also selects for Pocillopora coloniesover other available coral genera through the use of olfactory cues(Danilowicz, 1996), thus corroborating our results. The other speciesin our study C. parasema and C. octofasciatus appear to favour branchingAcropora species in their choice of living environment (Bonin et al.,2009, 2011; Pratchett and Berumen, 2008). However, this preferencewas not reflected in olfactory trials. This lack of response may be

apparent for a number of reasons. Either 1) olfactory cues are of littleimportance when discerning individual coral species, or, 2) the type ofcoral detected may be secondary to the presence of conspecifics andother environmental factors. The latter reason seems more likely, withthe gregarious nature of the study species is potentially to reinforcinghabitat associations with specific branching coral species (sensuGardiner and Jones, 2010).

Some limitations of the studymust be acknowledged. Previous stud-ies have shown evidence of rapid ontogenetic change in morphologyand behaviour at and/or soon after the point of settlement (Leis andYerman, 2012). Thus, preferences for coral speciesmay differ dependingon whether juveniles are tested before or after settlement (Danilowicz,1996). Since all our focal individuals had already settled, patterns ofchoicemay not necessarily reflect choices that weremade at settlement.However, almost all studies that have compared settlement choices inpre-settlement larvae and post-settlement juveniles have found identi-cal patterns, regardless of ontogenetic phase (e.g. Dixson et al., 2008;Öhman et al., 1998). For these species, therefore, it may be possible toinfer settlement choices in pre-settlement larvae through olfactory trialscarried out on post-settlement juveniles. In addition with regard to theconspecific treatments, we cannot certify that recruits are attracted spe-cifically toward the chemical cues of conspecifics, and not toward thechemical cues of fish in general. Future research will focus on testingconspecific and heterospecific cues against one another.

In conclusion, results of this study corroborate the importance ofolfactory cues in directing recruits towards appropriate habitats, par-ticularly towards the presence of conspecifics and areas of live coral.Despite apparent coral species-specific habitat preferences, olfactorycues do not appear to influence choice of live coral habitat type. Elu-cidating the mechanisms and strategies used in habitat selection isvital in attempting to predict how communities or individual speciesmay respond to the degradation of their environment (Hawkins et al.,2000; Jones et al., 2004; Swihart et al., 2003). A change in olfactorypreferences, or to the manner in which the fish perceives its sur-roundings is likely to impact subsequent distributions and abun-dance. The significant olfactory choices for both conspecifics andlive corals over water with no associated reef cues are likely to con-tribute to the patterns of declining reef fish abundance in responseto declining coral health through potential positive feedback mecha-nisms. In such cases, the degradation of the coral communities maylead to less recruitment, resulting in fewer settlers cueing towardsparticular sites at a later date. As a consequence the subsequent re-duction in conspecific presence will further deter potential recruits,and so on and so forth. This in turn could allude to critical changesin competition and behavioural interactions, consequently leadingto more widespread changes in coral reef assemblages.

Acknowledgements

Thanks to Danielle Dixson for assistance with the experimental de-sign, and the loan of the two-channel choice-flume, the staff atMahoniaNa Dari Research and Conservation Centre and the staff at WalindiPlantation Resort for logistical support. We greatly appreciate and ac-knowledge the traditional owners of the Tamare–Kilu reefs in KimbeBay for allowing access and use of their local reef resources in order tocarry out this investigation. Thanks also go to several anonymous re-viewers for their invaluable critique regarding the improvement of themanuscript. This work was supported by core funding to G. Jonesfrom the ARC Centre of Excellence for Coral Reef Studies. It was coveredunder James Cook University ethics approval number A1264. [RH]

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